JP2008-200442A (which will be hereinafter referred to as Reference 1) discloses a known seat reclining apparatus including a stepless adjustment mechanism. Reference 1 discloses how wedge members are pressed by an input member rotating the wedge members when the input member is driven by a motor. The input member is provided at an end portion of each of the wedge members in a circumferential direction of the wedge member. The input member is configured so that a pressing force line thereof is arranged between radially inward and outward contact points of the wedge member relative to first and second gear members, respectively (the first and second gear members correspond to first and second members). For example, when the input member is driven by the motor, the wedge member is pressed by the input member so as to rotate in a direction from a small-clearance portion to a large-clearance portion of an accommodating chamber (an accommodating space) formed by the first member and the second member. At this time, friction resistance of the wedge member may be minimized by the aforementioned configuration of the seat reclining apparatus of Reference 1. Additionally, a pressing point via which a pressing surface of the input member presses the wedge member is designed to be positioned at an outward side of the pressing surface in a radial direction of the pressing surface so that the pressing force line may be surely positioned between the radially inward and outward contact points of the wedge member even in a case dimensional variations in manufacturing occur.
However, according to the seat reclining apparatus disclosed in Reference 1, the end portion of the wedge member in the circumferential direction is pressed by the input member. Accordingly, the pressing point of the input member is located away from the radially inward and outward contact points. Therefore, for example, in a case where the radially inward contact point or the radially outward contact point may not be accurately arranged because of positional or dimensional errors of the accommodating chamber due to dimensional variations in manufacturing of the first member or the second member or in a case where the pressing force line may not be accurately arranged because of dimensional variations in manufacturing of the wedge member, the pressing force line is unlikely to be surely positioned between the radially inward and outward contact points. As a result, high manufacturing accuracy is required for each of the first member, the second member, and the wedge member of Reference 1.
JP2001-340154A (which will be hereinafter referred to as Reference 2) discloses a known seat reclining apparatus including a stepless adjustment mechanism in the same way as the seat reclining apparatus of Reference 1. A protruding portion extending in a direction of a central axial of an input member (a shaft) is formed at each of wedge members. In addition, when the input member is driven by a motor, the input member presses the protruding portion of the wedge member to thereby rotate the wedge member. Therefore, a shape of the input member may be simplified according to the seat reclining apparatus of Reference 1. Moreover, the wedge members are covered by an axial end surface of an annular flat portion (of a cam portion) of the input member, thereby being restricted from shifting in the direction of the central axis of the input member.
According to the seat reclining apparatus disclosed in Reference 2, a pressing point via which the input member presses the wedge member is arranged at the protruding portion of the wedge member; therefore, the pressing point is deviated from contact points (radially inward and outward contact points) of the wedge member relative to a gear plate (the first member) and an upper arm (the second member) in the direction of the central axis of the input member. Accordingly, depending on the setting of a pressing force line, an axial component of offset load may be applied to the wedge member. Consequently, when the wedge member is rotated by the input member driven by the motor, a load may be unevenly applied to inner and outer circumferential contact surfaces of the wedge member relative to the first member and the second member. As a result, the wedge member is partially worn, therefore disturbing the wedge member from smoothly rotating or sliding, deteriorating the strength of the wedge member, and generating noises when the wedge member rotates or slides.
A need thus exists for a seat reclining apparatus, which is not susceptible to the drawbacks mentioned above.